class EmailSever:
    __instance = None

    def __new__(cls, *args, **kwargs):
        """
        实现单例
        """
        if not isinstance(cls.__instance, cls):
            instance = super().__new__(cls, *args, **kwargs)
            cls.__instance = instance
        return cls.__instance


server = EmailSever()
server2 = EmailSever()
server3 = EmailSever()
